This invention relates to a swash-plate compressor and, in particular, to a swash-plate compressor comprising a swash plate coupled to a piston through a shoe slidably interposed therebetween.
A conventional swash plate compressor comprises a casing, a cylinder block formed in the casing and formed with a plurality of cylinder bores angularly spaced about an axis, a rotary shaft extending on the axis and rotatably supported in the casing, a swash plate attached to the rotary shaft to be rotated together with the rotary shaft, a plurality of pistons each having a head portion slidably fitted into the cylinder bore and a shoe receiving portion connected to the head portion, and a pair of shoes which are slidably disposed on the shoe receiving portion of the piston and kept in sliding contact with an outer periphery of the swash plate interposed between the shoes so that rotary motion of the rotary shaft is converted into a linear reciprocating motion of each piston through the swash plate and the shoes. The shoe receiving portion has a pair of shoe receiving recesses with spherically concave shoe receiving surfaces for receiving the shoes, respectively. Each of the shoes has a piston-side sliding surface of a spherical convex to be brought into sliding contact with each of the shoe receiving surfaces. On the other hand, each of the shoes has the opposite flat surface as a swash plate-side sliding surface which is in sliding contact with a flat surface of the swash plate.
In the conventional swash-plate compressor, the shoe receiving surface of the piston has a radius of curvature substantially equal to that of the piston-side sliding surface of the shoe.
Thus, in the conventional swash-plate compressor, the shoe receiving surface and the piston-side sliding surface have spherical shapes exactly coincident with each other. This means that substantially no clearance is produced between the shoe receiving surface and the piston-side sliding surface. Therefore, a mist of a lubricating oil contained in a refrigerant gas within the swash-plate compressor is hardly introduced between the shoe receiving surface and the piston-side sliding surface. In this event, lubrication between the shoe receiving surface and the piston-side sliding surface is insufficient. This often results in occurrence of seizure therebetween and in an increase in driving load of the compressor.